Adaptive power amplifier linearization in time division duplex communication systems

ABSTRACT

In an aspect of the invention, a method is performed in a transceiver for adaptive power amplifier linearization in time division duplex communication systems. The method comprises, in response to a first condition, performing, using a feedback signal generated by receiving subsystem circuitry, adaptive power amplifier linearization on a signal to be transmitted. The method additionally comprises, in response to a second condition, performing operations in order to determine receive data from a received radio frequency (RF) signal. The operations use at least the receiving subsystem circuitry. In a further aspect of the present invention, a transceiver is disclosed.

TECHNICAL FIELD

This invention relates generally to radio frequency communication and,more specifically, relates to adaptive power amplifier linearization.

BACKGROUND OF THE INVENTION

Power amplifiers are used in certain communication systems to boostamplitude of a transmitted signal to allow reliable reception by adistant receiver. All power amplifiers exhibit some nonlinearcharacteristics, and the nonlinear characteristics may be described byquantifying properties of AM/AM and AM/PM curves for the poweramplifier. An AM/AM curve represents input amplitude to output amplitudeconversion, while the AM/PM curve represents input amplitude to outputphase conversion. Nonlinearities caused by the nonlinear characteristicsof power amplifiers distort the spectrum of the transmitted signal,causing the bandwidth of the output signal of the power amplifier to bewider than the bandwidth of the input signal of the power amplifier.Consequently, some form of compensation technique is required to producea power efficient and bandwidth efficient communication system.

One of the compensation techniques used is power amplifierlinearization. Power amplifier linearization uses predistortion todistort (e.g., the amplitude, phase or both) the input signal of thepower amplifier so that, when combined with the amplifiercharacteristics, the concatenated input/output characteristic of boththe predistortion and the power amplifier is linear. The power amplifierlinearization can be either fixed or adaptive. Adaptive power amplifierlinearization techniques are the most practical, since these techniquescan adapt the predistortion to track changes in the characteristics ofthe power amplifier due to age, temperature, and other factors.

While there are benefits to adaptive power amplifier linearization,there are also problems associated therewith. It would therefore bedesirable to provide techniques that overcome these problems.

BRIEF SUMMARY OF THE INVENTION

The foregoing and other problems are overcome, and other advantages arerealized, in accordance with exemplary embodiments of these teachings.In particular, the present invention provides techniques for adaptivepower amplifier linearization for time division duplex communicationsystems.

In an aspect of the invention, a method is performed in a transceiverfor adaptive power amplifier linearization in time division duplexcommunication systems. The method comprises, in response to a firstcondition, performing, using a feedback signal generated by receivingsubsystem circuitry, adaptive power amplifier linearization on a signalto be transmitted. The method additionally comprises, in response to asecond condition, performing operations in order to determine receivedata from a received radio frequency (RF) signal. The operations use atleast the receiving subsystem circuitry.

In a further aspect of the present invention, a transceiver is disclosedthat comprises first and second inputs and first and second outputs. Thetransceiver additionally comprises adaptive power amplifierlinearization circuitry comprising first and second inputs and anoutput. The first input of the adaptive power amplifier linearizationcircuitry is coupled to the first input of the transceiver. The outputof the adaptive power amplifier linearization circuitry is coupled tothe first output of the transceiver. The transceiver also comprises afirst switch comprising first and second input terminals and an outputterminal. The first input terminal of the first switch is coupled to theoutput of the adaptive power amplifier linearization circuitry. Thesecond input terminal of the first switch coupled to the second input ofthe transceiver.

The transceiver also comprises receiving subsystem circuitry having aninput and an output. The input of the receiving subsystem circuitry iscoupled to the output terminal of the first switch. The transceiveradditionally has a second switch comprising first and second outputterminals and an input terminal. The input terminal of the second switchis coupled to the output of the receiving subsystem circuitry. The firstoutput terminal of the second switch is coupled to the second input ofthe adaptive power amplifier predistortion algorithm circuitry. Thesecond output terminal of the second switch is coupled to the secondoutput of the transceiver.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects of embodiments of this invention aremade more evident in the following Detailed Description of ExemplaryEmbodiments, when read in conjunction with the attached Drawing Figures,wherein:

FIG. 1 is a block diagram of an exemplary transmitter used to illustratepower amplifier linearization;

FIG. 2 is a block diagram of an exemplary transceiver used to illustrateadaptive power amplifier linearization;

FIG. 3 is a block diagram of an exemplary transceiver using adaptivepower amplifier linearization in accordance with an illustrativeembodiment of the present invention; and

FIG. 4 is method performed by a receiver that allows adaptive poweramplifier linearization in accordance with an exemplary embodiment ofthe present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

As previously described, power amplifier linearization is one techniqueused to reduce the effects of nonlinear characteristics of poweramplifiers. Shown in FIG. 1 is a transmitter 100 that comprises amodulator 110 coupled to power amplifier linearization circuitry 121.The power amplifier linearization circuitry 121 comprises predistortionalgorithm circuitry 120 and a power amplifier 130. The modulator 110modulates transmit data 105 through techniques such as linear pulseshaped modulation. The modulator 110 produces a modulated data signal115, which is coupled to the predistortion algorithm circuitry 120. Itis to be noted that signals are coupled though circuitry such as traceson a circuit board or wiring levels on a semiconductor. A signal istherefore typically considered to be separate from the circuitry onwhich the signal is placed. For clarity, however, signals will mainly bedescribed herein without regard to the circuitry on which the signalresides.

The predistortion algorithm circuitry 120 distorts the modulated datasignal 115 to create a distorted data signal 125 that is coupled to thepower amplifier 130. The power amplifier 130 produces an amplifiedtransmit radio frequency (RF) signal 135. The distortion caused by thepredistortion algorithm circuitry 120 occurs so that, when the distortedsignal 125 is combined with characteristics of the power amplifier 130,the input/output characteristic of the power amplifier linearizationcircuitry 121 is approximately linear. In other words, there is anapproximately linear relationship between the transmit signal 135 andthe modulated data signal 115.

Power amplifier linearization techniques performed by the poweramplifier linearization circuitry 121 can be either fixed or adaptive.As stated above, adaptive linearization techniques are the mostpractical, since these techniques can adapt distortion caused by thepredistortion algorithm circuitry 120 in order to track changes incharacteristics of the power amplifier 130 due to age, temperature, andother factors.

Turning now to FIG. 2, an exemplary transceiver 200 is shown that isused to illustrate adaptive power amplifier linearization. Transceiver200 comprises a transmitter 210 and a receiver 250. Transmitter 210comprises a modulator 215, adaptive power amplifier linearizationcircuitry 221, a tap 236, and dedicated receiving subsystem circuitry245. The adaptive power amplifier linearization circuitry 221 comprisesadaptive predistortion algorithm circuitry 225 and a power amplifier235. The receiver 250 comprises a low noise amplifier (LNA) 260,receiving subsystem circuitry 270, and a demodulator 280.

The modulator 215 modulates transmit data 205 through techniques such aslinear pulse shaped modulation. The modulator 215 produces a modulateddata signal 220, which is coupled to the adaptive predistortionalgorithm circuitry 225.

The adaptive predistortion algorithm circuitry 225 distorts themodulated data signal 220 to create a distorted data signal 230 that iscoupled to the power amplifier 235. The power amplifier 235 produces anamplified transmit RF signal 237, which is suitable for coupling to oneor more antennas (not shown). The input/output characteristic of theadaptive power amplifier linearization circuitry 221 is approximatelylinear. The dedicated receiving subsystem circuitry 245 is coupled tothe amplified transmit RF signal 237 through tap 236. Typically, a tap236 will reduce the power of the amplified transmit RF signal 237 toproduce a reduced power transmit RF signal 240. However, the dedicatedreceiving subsystem circuitry 245 can also reduce the power of theamplified transmit RF signal 237, if necessary. The dedicated receivingsubsystem circuitry 245 operates on the reduced power transmit RF signal240 and creates a feedback signal 247. The adaptive predistortionalgorithm circuitry 225 then compares the feedback signal 247 with themodulated data signal 220 (e.g., generally a delayed version of themodulated data signal 220) and updates characteristics of an adaptivepredistortion algorithm portion (not shown) based on the comparison.

On the receiver 250, the LNA 260 amplifies the received RF signal 255and creates an amplified received RF signal 265. The received RF signal255 is received from one or more antennas (not shown). The receivingsubsystem circuitry 270 operates on the amplified received RF signal 265and produces a received signal 275. The received signal 275 isdemodulated by demodulator 280 to produce receive data 285.

As FIG. 2 shows, an adaptive predistortion algorithm, implemented in theadaptive predistortion algorithm circuitry 225, must have some mechanismfor monitoring the output (e.g., the amplified transmit RF signal 237)of the power amplifier 235. However, transceiver designs such as the oneillustrated in FIG. 2 require a transmitter 210 with a dedicatedreceiving subsystem circuitry 245 to monitor the output of the poweramplifier 235. The dedicated receiving subsystem circuitry 245 addscomplexity and cost to the transceiver 200.

For communication systems where the transceiver 200 can transmit andreceive at the same time (e.g., the adaptive amplifier linearizationcircuitry 221 performs power amplifier linearization on the modulateddata signal 220 while the receiving subsystem circuitry 270 operates onor “listens” for the amplified received RF signal 265), then thededicated receiving subsystem circuitry 245 is useful. However, in atime-division duplex (TDD) communication system, a transceiver wouldhave an idle receiver when a corresponding transmitter is active.Typically, a TDD communication system would transmit for a period oftime then receive (e.g., “listen”) for a period of time, andtransmission of data and reception of data are generally mutuallyexclusive. Such TDD communication systems include time-divisionmultiplexing (TDM) systems and systems using a half-duplex link. Inthese communication systems, the transmitter 210 is typically activeduring the transmission of a data burst and typically inactive during asubsequent interval to allow reception of signals from othertransmitters. During burst transmission, the receiving subsystemcircuitry 270 is idle since the output of the power amplifier 235 duringthe burst swamps any other signal that may be present, thereby renderingreception unlikely or impossible. The idle receiving subsystem circuitry270 can be used to monitor the power amplifier output (e.g., amplifiedtransmit RF signal 237) for the purposes of adaptive power amplifierlinearization as described above. Such a system is illustrated in FIG.3.

Referring now to FIG. 3, an exemplary transceiver 300 is shown that isused to illustrate adaptive power amplifier linearization in accordancewith an illustrative embodiment of the present invention. Transceiver300 comprises a transmitter 310 and a receiver 350. Transmitter 310comprises a modulator 315, adaptive amplifier linearization circuitry321, a tap 336, and control circuitry 307. The adaptive amplifierlinearization circuitry 321 comprises adaptive predistortion algorithmcircuitry 325 and a power amplifier 335. The receiver 350 comprises alow noise amplifier (LNA) 360, receiving subsystem circuitry 370, ademodulator 380, switches 352 and 353, and control circuitry 351.

The modulator 315 comprises circuitry (not shown) that modulatestransmit data 305 through known modulation techniques such as linearpulse shaped modulation. The modulator 315 produces a modulated datasignal 320, which is coupled to the adaptive predistortion algorithmcircuitry 325.

The adaptive predistortion algorithm circuitry 325 distorts themodulated data signal 320 to create a distorted data signal 330 that iscoupled to the power amplifier 335. A reference describing that someform of compensation technique is required to produce a power efficientand bandwidth efficient system is A. Katz, “Linearization: ReducingDistortion in Power Amplifiers,” IEEE Microwave Magazine, pp. 37-49,December 2001, the disclosure of which is hereby incorporated byreference. The power amplifier 335 produces an amplified transmit RFsignal 337, which is suitable for coupling to one or more antennas (notshown). The input/output characteristic of the adaptive power amplifierlinearization circuitry 321 is approximately linear.

In an exemplary embodiment, the switches 352 and 353 are switched to theA positions when the transmitter 310 is in an active state. When theswitches 352 and 353 are switched to the A positions, signals are routedfrom the amplified transmit RF signal 337 to and through the receivingsubsystem circuitry 370 and to the adaptive predistortion algorithmcircuitry 325. Typically, a tap 236 will reduce the power of theamplified transmit RF signal 337 to produce a reduced power transmit RFsignal 340 that is coupled to input A of the switch 353. However, thereceiving subsystem circuitry 370 can also reduce the power of theamplified transmit RF signal 337, routed through output 367 of theswitch 353, if desired. The receiving subsystem circuitry 370 operateson the reduced power transmit RF signal 340 and creates a feedbacksignal 347 that is coupled to the input 348 of the switch 352 to theadaptive predistortion algorithm circuitry 325.

The adaptive predistortion algorithm circuitry 325 then compares thefeedback signal 347 with the modulated data signal 320 (e.g., generallya delayed version of the modulated data signal 320) and updatescharacteristics of an adaptive predistortion algorithm portion (notshown) of the adaptive predistortion algorithm circuitry 325 based onthe comparison.

In an exemplary embodiment, when the transmitter 310 is idle, theswitches 352 and 353 are switched to the B positions. In thesepositions, the LNA 260 amplifies the received RF signal 355 and createsan amplified received RF signal 365. The amplified received RF signal365 is coupled to the receiving subsystem circuitry 370 through theoutput 367 of the switch 353. The receiving subsystem circuitry 370 canreceive transmissions (e.g., burst transmissions) from othertransmitters. The receiving subsystem circuitry 370 operates on theamplified received RF signal 365 and produces received signal 375 thatis routed to the input 348 of the switch 352 to the demodulator 380. Thereceived signal 375 is demodulated by demodulator 380 to produce receivedata 385.

The approach shown in FIG. 3 has a “dual use” of the receiving subsystemcircuitry 370. This dual use eliminates the need for a separatereceiving subsystem circuitry (e.g., dedicated receiving subsystemcircuitry 245 of FIG. 2) dedicated exclusively to monitoring the output(e.g., amplified transmit RF signal 337) of the power amplifier 335.

Switches 352 and 352 are controlled, e.g., in a coordinated fashion, bythe control circuitry 351 through control signal 354. The switches canbe any device suitable for coupling a signal from a first terminal toone of a plurality of second terminals. Thus, switches could be,illustratively, relays, two or more transistors, multiplexers, and somecombination of two or more of these. In the example of FIG. 3, controlcircuitry 307 communicates a state of the transmitter 310 through aconnection 345 to control circuitry 351. For instance, a zero onconnection 351 could correspond to “active” and a one on connection 351could correspond to “idle.” In response to the state of the transmitter,the control circuitry 351 coordinates switching of the two switches 352and 353 into appropriate positions A or B.

The control circuitries 307 and 308 may be combined into one circuit orcould be further distributed into smaller circuitry. Additionally, it isnot necessary for a “state” of a transmitter to be known. For instance,control circuitries 307 and 308 could be clock circuitry implemented toallow the transmitter 310 to transmit for a first time period (e.g.,during which the switches 352 and 353 would be in position A) and toallow the receiver 350 to receive for a second time period (e.g., duringwhich the switches 352 and 353 would each be in position B).

Furthermore, an active state of transmitter 310 typically means that thetransmitter 310 is transmitting. However, the transmitter 310 may bepreparing to transmit when the transmitter 310 is in an active state butthe receiver 350 could be receiving transmissions from othertransmitters when the transmitter 310 is in the active state but nottransmitting. For simplicity, it is assumed herein that, in response tothe transmitter being in the active state, the control circuitry 351will switch each of the switches 352 and 353 to position A, and that, inresponse to the transmitter being in an idle state, the controlcircuitry 351 will switch each of the switches 352 and 352 to positionB. It should be noted that the switches 352 and 353 need not be switchedto position A for the entire period that the transmitter 310 istransmitting. However, it will typically be the case that the switches352 and 353 are switched to position A for at least the entire periodthat the transmitter 310 is transmitting.

The transceiver 300 may be implemented in many different ways known tothose skilled in the art, and the receiving subsystem circuitry 370,depending on the implementation of the transceiver 300, performsoperations known to those skilled in the art to convert a signal on theoutput 367 of the switch 353 into the feedback signal 347 and thereceived signal 375. For instance, the modulator 315 could be a basebandmodulator with linear pulse shaped modulation and the receivingsubsystem circuitry 370 could comprise a matched filter (not shown) anda nonlinear equalizer (not shown).

As another example, the modulator 315 could be a baseband modulator andthe adaptive power amplifier linearization circuitry 321 could comprisepulse shaping circuitry intermediate the adaptive predistortionalgorithm circuitry 325 and the power amplifier 335. In the latterexample, the receiving subsystem circuitry 370 could again comprise amatched filter and a nonlinear equalizer. See, for instance, an articleby A. Behravan et al., entitled “Adaptive Predistorter Design forNonlinear High Power Amplifiers,” Proc. of GHz 2003 Symposium,Linköping, Sweden (November 2003), the disclosure of which is herebyincorporated by reference. Behravan describes non-adaptive poweramplifier linearization, but without the dual use design of FIG. 3.

As yet another example, the adaptive power amplifier linearizationcircuitry 321 could comprise a digital-to-analog converter (DAC) (notshown) that is intermediate the adaptive predistortion algorithmcircuitry 325 and the power amplifier 335. The modulator 315 could bemoved into the adaptive power amplifier linearization circuitry 321,placed after the DAC, and adapted to perform up-conversion. Thereceiving subsystem circuitry 370 could then comprise the demodulator380 (adapted also to perform down-conversion) and analog-to-digitalconversion (ADC). The adaptive predistortion algorithm circuitry 325could also comprise (not shown) an adaptation algorithm section, alook-up table section, a delay, and a complex gain adjustment section.The adaptation algorithm section compares the transmit data 305 (afterpassing through the delay) with the feedback signal 347 and modifiesvalues in the lookup table section (which also has input from thetransmit data 305). The complex gain adjustment section has input fromthe look-up table section and performs the distortion of the transmitdata 305 to create the distorted data signal 330. See, for instance, K.Mekechuk et al., “Linearizing Power Amplifiers Using DigitalPredistortion, EDA Tools and Test Hardware,” High Frequency Electronics,pp. 18-24, April 2004, the disclosure of which is hereby incorporated byreference. Mekechuk describes non-adaptive power amplifierlinearization, without the dual use design of FIG. 3, but the techniquesin Mekechuk also have been applied to adaptive power amplifierlinearization.

Additional examples of predistortion and associated communicationsystems are found in the following references, the disclosures of whichis hereby incorporated by reference: (1) Y. Akawa and Y. Nagata, “HighlyEfficient Digital Mobile Communications with a Linear ModulationMethod,” IEEE Journal on Selected Areas in Communication, vol. SAC-5,pp. 890-895, June 1987; (2) A. Bateman, D. Haines, and R. Wilkinson,“Linear Transceiver Architectures,” in Proc. of the IEEE VehicularTechnology Conf., pp. 478-484, 1988; (3) S. Ono, N. Kondoh, and Y.Shimazaki, “Digital Cellular System With Linear Modulation,” in Proc. ofthe IEEE Vehicular Technology Conf., pp. 44-49, 1989; (4) M. Nannicini,P. Magni, and F. Oggioni, “Temperature Controlled Predistortion Circuitsfor 64 QAM Microwave Power Amplifiers,” IEEE Microwave Theory TechnicalDigest, pp. 99-102, 1985; (5) J. Hamiki, “An Automatically ControlledPredistorter for Multilevel Quadrature Amplitude Modulation,” IEEETransactions on Communications, vol. COM-31, pp. 707-712, May 1983; (6)H. Girard and K. Feher, “A New Baseband Linearizer for More EfficientUtilization of Earth Station Amplifiers Used for QPSK Transmission,”IEEE Journal on Selected Areas in Communications, vol. SAC-1, pp. 46-56,January 1983; (7) J. Graboski and R. Davis, “An Experimental MQAM MODEMUsing Amplifier Linearization and Baseband Equalization Techniques,” inProc. of the National Communications Conference, pp. E3.2.1-E3.2.6,1982; (8) A. Saleh and J. Salz, “Adaptive Linearization of PowerAmplifiers in Digital Radio Systems,” Bell Systems Technical Journal,vol. 62, no. 4, pp. 1019-1033, April 1983; and (9) Y. Nagata, “LinearAmplification Technique for Digital Mobile Communications,” in Proc. ofthe IEEE Vehicular Technology Conference, pp. 159-164, 1989.

The transmitter 310 and receiver 350 may comprise additional componentsknown to those skilled in the art. For instance, coding circuitry (notshown) for block or convolutional coding may be added to the transmitter310 and corresponding decoding circuitry (not shown) may be added to thereceiver 350.

Furthermore, as used herein, the term “circuitry” can include one ormore processors, such as digital signal processors (DSPs), that areprogrammed using instructions to perform the functions described herein.Such processors are typically coupled to one or more memories.Additionally, “circuitry” could comprise a combination of a processorand hardware elements, where the processor performs certain functionsdescribed herein and the hardware elements performs additional functionsdescribed herein. Such hardware elements could be discrete devices,integrated circuits, such as very large scale integrated (VLSI)circuits, gate arrays, or a combination of two or more of these. Thecircuitry may also include memory. As is known in the art, embodimentsof the present invention may be provided as part of a signal bearingmedium tangibly embodying a program of machine-readable instructionsexecutable by a processor to perform one or more operations describedherein.

Turning now to FIG. 4 with appropriate reference to FIG. 3, a method 400is shown that is performed by receiver 350 of FIG. 3 and that allowsadaptive power amplifier linearization in accordance with an exemplaryembodiment of the present invention. Method 400 begins in step 405 whenthe state of the transmitter 310 is determined. The state of thetransmitter 310 may be determined, as described above, in an exemplaryembodiment when connection 345 is sampled by control circuitry 351 ofthe receiver 350. If the state of the transmitter 310 is “Active,” steps410-425 are performed. In step 410, the receiving subsystem circuitry370 is coupled (e.g., by the switch 353) to the amplified transmit RFsignal 337. In step 415, the receiving subsystem circuitry 370 convertsthe reduced power RF transmit signal 340 to the feedback signal 347. Instep 420, the feedback signal 347 is coupled to the adaptivepredistortion algorithm circuitry 325 (e.g., through the switch 352). Instep 425, if there is no state change (step 425=No), then steps 410through 420 are performed again. Typically, the first time step 410 isperformed, the switch 353 will be changed to position A, and theposition of switch 353 will not change until a state change in step 425(step 425=Yes). Similarly, the first time step 420 is performed, theswitch 352 will be changed to position A, and the position of switch 352will not change until state change in step 425 (step 425=Yes). Whenthere is a state change (step 425=Yes), the method continues in step405. Note that steps 410-425 can be considered to correspond to an idlestate of the receiver 350.

If the state of the transmitter 310 is “Idle,” steps 430-445 areperformed. In step 430, the receiving subsystem circuitry 370 is coupled(e.g., by the switch 353) to the amplified received RF signal 365. Instep 435, the receiving subsystem circuitry 370 converts the amplifiedreceived RF signal 365 to the received signal 375. In step 440, thereceived signal 375 is coupled (e.g., through the switch 352) to thedemodulator 380 (e.g., or as the receive data 385 on an output of thereceiver 350). In step 445, if there is no state change (step 445=No),then steps 430 through 440 are performed again. Typically, the firsttime step 430 is performed, the switch 353 will be changed to position Band the position of switch 353 will not change until a state change instep 445 (step 445=Yes). Similarly, the first time step 440 isperformed, the switch 352 will be changed to position B and the positionof switch 352 will not change until state change in step 445 (step445=Yes). When there is a state change (step 445=Yes), the methodcontinues in step 405.

Typically, steps 415 and 435 should perform the same conversion.However, there may be implementations when there are differences betweenhow the amplified transmit RF signal 337 (e.g., as the reduced power RFtransmit signal 340) is converted to the feedback signal 347 and how theamplified received RF signal 365 is converted to the received signal375. These differences could be resolved by modifying the receivingsubsystem circuitry 370 to perform certain operations in response to theswitches 352 and 353 being in certain positions (e.g., or in response tothe control signal 354) or could be performed by additional circuitryimplemented, for example, intermediate the tap 336 and the A position ofthe switch 353. Although typically not the case, there may also bedifferences in the feedback signal 347 and the received signal 375.These latter differences may be could be resolved by modifying thereceiving subsystem circuitry 370 to perform certain operations inresponse to the switches 352 and 353 being in certain positions (e.g.,or in response to the control signal 354) or could be performed byadditional circuitry implemented, for example, intermediate thereceiving subsystem circuitry 370 and the adaptive predistortionalgorithm circuitry 325.

It should also be noted, as stated above, that there may be no actualdetermination of the state of the transmitter 310 (step 405). Instead,steps 410-420 could be performed for a first predetermined time periodthen steps 430-440 would be performed for a second predetermined timeperiod. In fact, there could be two conditions used to control method400: during a first condition (e.g., a first state of the transmitter310 or of the receiver 350, or a first time period for transmission),then receiving subsystem circuitry would be coupled to the amplifiedtransmit RF signal (step 410); during a second condition (e.g., a secondstate of the transmitter 310 or of the receiver 350, or a second timeperiod for reception), then receiving subsystem circuitry would becoupled to the amplified received RF signal (step 430). Additionally,there may be more than two states of the transmitter 405 (e.g.,“Active-Transmitting”; “Active-Creating Initial Data for Transmitting”;and “Idle”). Also, adaptive power amplifier linearization need not beperformed every time a transmission is performed and, instead, adaptivepower amplifier linearization could be performed periodically in termsof transmissions (e.g., adaptive power amplifier linearization could beperformed every third transmission).

The foregoing description has provided by way of exemplary andnon-limiting examples a full and informative description of the bestmethod and apparatus presently contemplated by the inventors forcarrying out the invention. However, various modifications andadaptations may become apparent to those skilled in the relevant arts inview of the foregoing description, when read in conjunction with theaccompanying drawings and the appended claims. Nonetheless, all such andsimilar modifications of the teachings of this invention will still fallwithin the scope of this invention.

Furthermore, some of the features of the preferred embodiments of thisinvention could be used to advantage without the corresponding use ofother features. As such, the foregoing description should be consideredas merely illustrative of the principles of the present invention, andnot in limitation thereof.

1. In a transceiver, a method for adaptive power amplifier linearizationin time division duplex communication systems, comprising: in responseto a first condition: using a feedback signal generated by receivingsubsystem circuitry, to perform adaptive power amplifier linearizationon a signal to be transmitted, where using the feedback signal comprisescomparing the feedback signal to a modulated data signal and updatingcharacteristics of an adaptive predistortion algorithm based on thecomparison; and in response to a second condition: performing operationsin order to determine receive data from a received radio frequency (RF)signal, the operations using at least the receiving subsystem circuitry.2. The method of claim 1, wherein the first and second conditions aremutually exclusive.
 3. The method of claim 1, wherein: in response tothe first condition, decoupling the received RF signal from thereceiving subsystem circuitry so that receive data cannot be determinedfrom the received RF signal; and in response to the second condition,not performing adaptive power amplifier linearization.
 4. The method ofclaim 1, wherein: the signal to be transmitted is received from a firstinput of the transceiver; performing adaptive power amplifierlinearization on the signal to be transmitted results in an amplifiedtransmit RF signal; in response to the first condition: coupling theamplified transmit RF signal to a receiving subsystem; converting, usingthe receiving subsystem circuitry, the amplified transmit RF signal tothe feedback signal; coupling the feedback signal to adaptive poweramplifier linearization circuitry, the adaptive power amplifierlinearization circuitry performing the adaptive power amplifierlinearization; and outputting the amplified transmit RF signal to afirst output of the transceiver; and in response to the secondcondition: receiving the received RF signal from a second input of thetransceiver; coupling the received RF signal to the receiving subsystemcircuitry; converting, using the receiving subsystem circuitry, thereceived RF signal to a received signal suitable for use in determiningthe receive data; and coupling the received signal to a second output ofthe transceiver.
 5. The method of claim 1, wherein the transceivercomprises: a transmission portion that performs the adaptive poweramplifier linearization on the signal to be transmitted; and a receptionportion that performs the operations in order to determine receive datafrom the received RF signal and that comprises the receiving subsystemcircuitry.
 6. The method of claim 5, wherein the first conditioncomprises the transmission portion being in a first state, and whereinthe second condition comprises the transmission portion being in asecond state.
 7. The method of claim 5, wherein the first conditioncomprises the transmission portion transmitting data, and wherein thesecond condition comprises the transmission portion not transmittingdata.
 8. A method for adaptive power amplifier linearization in timedivision duplex communication systems, comprising: in response to afirst condition: using a feedback signal generated by receivingsubsystem circuitry, to perform adaptive power amplifier linearizationon a signal to be transmitted; in response to a second condition:performing operations in order to determine receive data from a receivedradio frequency (RF) signal, the operations using at least the receivingsubsystem circuitry, wherein the transceiver comprises a transmissionportion that performs the adaptive power amplifier linearization on thesignal to be transmitted; a reception portion that performs theoperations in order to determine receive data from the received RFsignal and that comprises the receiving subsystem circuitry; the methodfurther comprising: determining a number of times the transmissionportion has transmitted data since a predetermined point; anddetermining if the number of times the transmission portion hastransmitted data is a predetermined number of times, wherein the firstcondition comprises the transmitter transmitting data for thepredetermined number of times and the second condition comprises thetransmitter not transmitting data.
 9. The method of claim 5, wherein thefirst condition comprises the receiving portion being in a first stateand wherein the second condition comprises the receiving portion beingin a second state.
 10. The method of claim 1, wherein the firstcondition comprises a first time period scheduled for performingadaptive power amplifier linearization, and wherein the second conditioncomprises a second time period scheduled for performing operations inorder to determine receive data from the received RF signal.
 11. Themethod of claim 10, wherein the method further comprises transmittingdata, and wherein performing adaptive power amplifier linearization isperformed when transmitting data.
 12. A transceiver comprising: firstand second inputs; first and second outputs; adaptive power amplifierlinearization circuitry comprising first and second inputs and anoutput, the first input of the adaptive power amplifier linearizationcircuitry coupled to the first input of the transceiver, the output ofthe adaptive power amplifier linearization circuitry coupled to thefirst output of the transceiver; a first switch comprising first andsecond input terminals and an output terminal, the first input terminalof the first switch coupled to the output of the adaptive poweramplifier linearization circuitry, the second input terminal of thefirst switch coupled to the second input of the transceiver; receivingsubsystem circuitry having an input and an output, the input of thereceiving subsystem circuitry coupled to the output terminal of thefirst switch; and a second switch comprising first and second outputterminals and an input terminal, the input terminal of the second switchcoupled to the output of the receiving subsystem circuitry, the firstoutput terminal of the second switch coupled to the second input of theadaptive power amplifier predistortion algorithm circuitry, and thesecond output terminal of the second switch coupled to the second outputof the transceiver.
 13. The transceiver of claim 12, wherein: thereceiving subsystem circuitry is adapted to convert a signal provided bythe output terminal of the first switch into a first signal suitable forcoupling to the second input of the adaptive power amplifierlinearization circuitry and for use in determining receive data; and theadaptive power amplifier linearization circuitry is adapted to distort,by using at least the first signal, a second signal from the first inputand adapted to amplify the second signal, wherein the distortion andamplification create a third signal on the output of the adaptive poweramplifier linearization circuitry and create an approximately linearrelationship between the second and third signals.
 14. The transceiverof claim 13, wherein the adaptive power amplifier linearizationcircuitry further comprises: adaptive predistortion algorithm circuitrycomprising two inputs and an output, the first input of the adaptivepredistortion algorithm circuitry coupled to the first input of theadaptive power amplifier linearization circuitry, the second input ofthe adaptive predistortion algorithm circuitry coupled to the secondinput of the adaptive power amplifier linearization circuitry, theadaptive predistortion algorithm circuitry adapted to distort, by usingat least the first signal, the second signal to create a fourth signalon the output of the adaptive predistortion algorithm circuitry; and apower amplifier comprising an input and an output, the input of thepower amplifier coupled to the output of the adaptive predistortionalgorithm circuitry, the output of the power amplifier coupled to theoutput of the adaptive power amplifier linearization circuitry, thepower amplifier adapted to amplify the fourth signal and adapted toproduce the third signal.
 15. The transceiver of claim 12, wherein: thefirst switch couples the first input terminal of the first switch to theoutput terminal of the first switch in a first position and couples thesecond input terminal of the first switch to the first output terminalof the first switch in a second position; and the second switch couplesthe input terminal of the second switch to the first output terminal ofthe second switch in the first position and couples the input terminalof the second switch to the second output terminal of the second switchin the second position.
 16. The transceiver of claim 15, furthercomprising control circuitry coupled to the first and second switches,the control circuitry adapted to switch both the first and secondswitches between the first and second positions.
 17. The transceiver ofclaim 16, wherein the control circuitry is further adapted to switchboth the first and second switches into the first position for a firsttime period and to switch both the first and second switches into thesecond position for a second time period.
 18. The transceiver of claim16, wherein: the control circuitry is further adapted to switch both thefirst and second switches from the second position to the first positionbased on a first state of transmission, and is further adapted to switchboth the first and second switches from the first position to the secondposition based on a second state of transmission.
 19. The transceiver ofclaim 16, wherein: the first state of transmission corresponds totransmitting data; and the second state of transmission corresponds toreceiving data and not transmitting data.
 20. The transceiver of claim12, further comprising: a modulator intermediate and coupled to thefirst input and the input of the adaptive power amplifier linearizationcircuitry; a low noise amplifier intermediate and coupled to the secondinput and the second input terminal of the first switch; and ademodulator intermediate and coupled to the second output terminal ofthe second switch and the second output.